Pigmented villonodular synovitis presenting as a baker cyst.

Pigmented villonodular synovitis (PVNS), a rare hyperproliferation of the synovial lining, commonly mimics other conditions. As a result, the diagnosis may remain elusive, as the classic signs of tenderness and effusion are not specific. Occasionally, PVNS presents as a popliteal cyst, which may divert attention from intra-articular pathology. In this article, we describe a case of PVNS that presented with a popliteal cyst as the chief problem report. In other cases PVNS presented as a popliteal cyst, and evidence was reported of PVNS within the cyst stalk and presumable intra-articular involvement. Our case did not present this way. We recommend that the diagnosis of PVNS be considered in young adults who present with a popliteal cyst.